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Date: Thu, 21 Feb 2013 20:33:27 -0600
From: Kim Phillips <kim.phillips@...escale.com>
To: Nicolas Pitre <nico@...xnic.net>
CC: "Woodhouse, David" <david.woodhouse@...el.com>,
Russell King - ARM Linux <linux@....linux.org.uk>,
Borislav Petkov <bp@...en8.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Daniel Santos <daniel.santos@...ox.com>,
David Rientjes <rientjes@...gle.com>,
Rusty Russell <rusty@...tcorp.com.au>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Rob Herring <robherring2@...il.com>
Subject: Re: [RFC] arm: use built-in byte swap function
On Thu, 21 Feb 2013 11:40:54 -0500
Nicolas Pitre <nico@...xnic.net> wrote:
> On Thu, 21 Feb 2013, Kim Phillips wrote:
>
> > On Wed, 20 Feb 2013 23:29:58 -0500
> > Nicolas Pitre <nico@...xnic.net> wrote:
> >
> > > On Wed, 20 Feb 2013, Kim Phillips wrote:
> > >
> > > > On Wed, 20 Feb 2013 10:43:18 -0500
> > > > Nicolas Pitre <nico@...xnic.net> wrote:
> > > >
> > > > > On Wed, 20 Feb 2013, Woodhouse, David wrote:
> > > > > > On Wed, 2013-02-20 at 09:06 -0500, Nicolas Pitre wrote:
> > > > > > > ... in which case there is no harm shipping a .c file and trivially
> > > > > > > enforcing -O2, the rest being equal.
> > > > > >
> > > > > > For today's compilers, unless the wind changes.
> > > > >
> > > > > We'll adapt if necessary. Going with -O2 should remain pretty safe anyway.
> > > >
> > > > Alas, not so for gcc 4.4 - I had forgotten I had tested
> > > > Ubuntu/Linaro 4.4.7-1ubuntu2 here:
> > > >
> > > > https://patchwork.kernel.org/patch/2101491/
> > > >
> > > > add -O2 to that test script and gcc 4.4 *always* emits calls to
> > > > __bswap[sd]i2, even with -march=armv6k+.
> >
> > argh, sorry - that script was testing support for
> > __builtin_bswap{16,32,64} directly, which isn't the same as testing
> > code generation of a byte swap pattern in C.
>
> Still, I'm not as confident as I was about this.
which part exactly? Having -O2 as "protection"? Yes, me neither.
> > I'll still try the assembly approach - gcc 4.4's armv6 output looks
> > worse than both the pre-armv6 and post-armv6 __arch_swab32
> > implementations currently in use:
> >
> > mov ip, sp
> > push {fp, ip, lr, pc}
> > sub fp, ip, #4
>
> You should use -fomit-frame-pointer to compile this. We don't need a
> frame pointer here, especially for a leaf function that the compiler
> decides to call on its own.
>
> > and r2, r0, #65280 ; 0xff00
> > lsl ip, r0, #24
> > orr r1, ip, r0, lsr #24
> > and r0, r0, #16711680 ; 0xff0000
> > orr r3, r1, r2, lsl #8
> > orr r0, r3, r0, lsr #8
>
> Other than that, it is true that the above is slightly suboptimal.
Here's the asm version I'm working on now, based on compiler
output of the C version. Haven't tested beyond defconfig builds,
which pass ok.
Is there anything I have to do for thumb mode? If so, how to test?
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dedf02b..e8a41d0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -59,6 +59,7 @@ config ARM
select CLONE_BACKWARDS
select OLD_SIGSUSPEND3
select OLD_SIGACTION
+ select ARCH_USE_BUILTIN_BSWAP
help
The ARM series is a line of low-power-consumption RISC chip designs
licensed by ARM Ltd and targeted at embedded applications and
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 5cad8a6..a277e97 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -108,12 +108,12 @@ endif
targets := vmlinux vmlinux.lds \
piggy.$(suffix_y) piggy.$(suffix_y).o \
- lib1funcs.o lib1funcs.S ashldi3.o ashldi3.S \
+ lib1funcs.o lib1funcs.S ashldi3.o ashldi3.S bswapsdi2.o \
font.o font.c head.o misc.o $(OBJS)
# Make sure files are removed during clean
extra-y += piggy.gzip piggy.lzo piggy.lzma piggy.xzkern \
- lib1funcs.S ashldi3.S $(libfdt) $(libfdt_hdrs)
+ lib1funcs.S ashldi3.S bswapsdi2.o $(libfdt) $(libfdt_hdrs)
ifeq ($(CONFIG_FUNCTION_TRACER),y)
ORIG_CFLAGS := $(KBUILD_CFLAGS)
@@ -155,6 +155,12 @@ ashldi3 = $(obj)/ashldi3.o
$(obj)/ashldi3.S: $(srctree)/arch/$(SRCARCH)/lib/ashldi3.S
$(call cmd,shipped)
+# For __bswapsi2, __bswapdi2
+bswapsdi2 = $(obj)/bswapsdi2.o
+
+$(obj)/bswapsdi2.S: $(srctree)/arch/$(SRCARCH)/lib/bswapsdi2.S
+ $(call cmd,shipped)
+
# We need to prevent any GOTOFF relocs being used with references
# to symbols in the .bss section since we cannot relocate them
# independently from the rest at run time. This can be achieved by
@@ -176,7 +182,8 @@ if [ $(words $(ZRELADDR)) -gt 1 -a "$(CONFIG_AUTO_ZRELADDR)" = "" ]; then \
fi
$(obj)/vmlinux: $(obj)/vmlinux.lds $(obj)/$(HEAD) $(obj)/piggy.$(suffix_y).o \
- $(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) FORCE
+ $(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) \
+ $(bswapsdi2) FORCE
@$(check_for_multiple_zreladdr)
$(call if_changed,ld)
@$(check_for_bad_syms)
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index 60d3b73..ba578f7 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -35,6 +35,8 @@ extern void __ucmpdi2(void);
extern void __udivsi3(void);
extern void __umodsi3(void);
extern void __do_div64(void);
+extern void __bswapsi2(void);
+extern void __bswapdi2(void);
extern void __aeabi_idiv(void);
extern void __aeabi_idivmod(void);
@@ -114,6 +116,8 @@ EXPORT_SYMBOL(__ucmpdi2);
EXPORT_SYMBOL(__udivsi3);
EXPORT_SYMBOL(__umodsi3);
EXPORT_SYMBOL(__do_div64);
+EXPORT_SYMBOL(__bswapsi2);
+EXPORT_SYMBOL(__bswapdi2);
#ifdef CONFIG_AEABI
EXPORT_SYMBOL(__aeabi_idiv);
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index af72969..5383df7 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -13,7 +13,7 @@ lib-y := backtrace.o changebit.o csumipv6.o csumpartial.o \
ashldi3.o ashrdi3.o lshrdi3.o muldi3.o \
ucmpdi2.o lib1funcs.o div64.o \
io-readsb.o io-writesb.o io-readsl.o io-writesl.o \
- call_with_stack.o
+ call_with_stack.o bswapsdi2.o
mmu-y := clear_user.o copy_page.o getuser.o putuser.o
diff --git a/arch/arm/lib/bswapsdi2.S b/arch/arm/lib/bswapsdi2.S
new file mode 100644
index 0000000..e9c8ca7
--- /dev/null
+++ b/arch/arm/lib/bswapsdi2.S
@@ -0,0 +1,36 @@
+#include <linux/linkage.h>
+
+#if __LINUX_ARM_ARCH__ >= 6
+ENTRY(__bswapsi2)
+ rev r0, r0
+ bx lr
+ENDPROC(__bswapsi2)
+
+ENTRY(__bswapdi2)
+ rev r3, r0
+ rev r0, r1
+ mov r1, r3
+ bx lr
+ENDPROC(__bswapdi2)
+#else
+ENTRY(__bswapsi2)
+ eor r3, r0, r0, ror #16
+ lsr r3, r3, #8
+ bic r3, r3, #65280 @ 0xff00
+ eor r0, r3, r0, ror #8
+ mov pc, lr
+ENDPROC(__bswapsi2)
+
+ENTRY(__bswapdi2)
+ mov ip, r1
+ eor r3, ip, ip, ror #16
+ eor r1, r0, r0, ror #16
+ lsr r1, r1, #8
+ lsr r3, r3, #8
+ bic r3, r3, #65280 @ 0xff00
+ bic r1, r1, #65280 @ 0xff00
+ eor r1, r1, r0, ror #8
+ eor r0, r3, ip, ror #8
+ mov pc, lr
+ENDPROC(__bswapdi2)
+#endif
Thanks,
Kim
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